Sleep Cyclic Alternating Pattern (CAP) as a Neurophysiological Marker of Brain Health

Quantitative methods to evaluate data acquired from polysomnography (PSG) may be sensitive to physiological and behavioral patterns including insomnia, cognition, psychiatric disorders, neurodegenerative diseases, and other aspects of daily function. Further, PSG analytic tools may provide insight into both systemic and acquired neurological disease. Reliable and valid quantitative tools sensitive to neurobehavioral states and outcomes may be valuable as biomarkers for intervention studies targeting sleep disruption. Disruptions in slow-wave sleep have been implicated in a variety of psychiatric, cognitive, and neurodegenerative disorders including post-traumatic stress disorder (PTSD) and Alzheimer’s disease. Cyclic alternating pattern (CAP) is a periodic activity within non-rem (NREM) sleep that may be an indicator of NREM instability. Components of CAP have been shown to be related to the next morning cognitive function including processing speed and divergent reasoning. Further, CAP has been shown to be associated with the occurrence of nightmares, a critical symptom of anxiety related conditions such as post-traumatic stress disorder. Calculating CAP currently requires specialized knowledge and tools, along with a full polysomnography (PSG) assessment making it largely inaccessible in a broad way, even within standard PSG clinics. Developing and using automated tools and wearable technology may accelerate the utility of quantitative PSG tools such as CAP as markers of disease and intervention targets. In this chapter, we review the current state of the literature on the application of cyclic alternating pattern (CAP) analyses to measuring slow-wave sleep stability and the relationship of CAP to systemic and brain outcomes.